As the only surviving adult son of Charlemagne and Hildegard, he became the sole ruler of the Franks after his father's death in 814, a position which he held until his death, save for the period 833–34, during which he was deposed.

During his reign in Aquitaine, Louis was charged with the defence of the empire's southwestern frontier. He conquered Barcelona from the Muslims in 801 and asserted Frankish authority over Pamplona and the Basques south of the Pyrenees in 812. As emperor he included his adult sons, Lothair, Pepin, and Louis, in the government and sought to establish a suitable division of the realm among them. The first decade of his reign was characterised by several tragedies and embarrassments, notably the brutal treatment of his nephew Bernard of Italy, for which Louis atoned in a public act of self-debasement.

In the 830s his empire was torn by civil war between his sons, only exacerbated by Louis's attempts to include his son Charles by his second wife in the succession plans. Though his reign ended on a high note, with order largely restored to his empire, it was followed by three years of civil war. Louis is generally compared unfavourably to his father, though the problems he faced were of a distinctly different sort.

Louis was crowned King of Aquitaine as a child in 781[3] and sent there with regents and a court. Charlemagne constituted the sub-kingdom in order to secure the border of his kingdom after the destructive war against the Aquitanians and Basques under Waifer (capitulated c. 768) and later Hunald, which culminated in the disastrous Battle of Roncesvalles (778). Charlemagne wanted his son Louis to grow up in the area where he was to reign. However, in 785, wary of the customs his son may have been taking in Aquitaine, Charlemagne sent for him to Aquitaine and Louis presented himself at the Royal Council of Paderborn dressed up in Basque costumes along with other youths in the same garment, which may have made a good impression in Toulouse, since the Basques of Vasconia were a mainstay of the Aquitanian army.

In 794, Charlemagne settled four former Gallo-Roman villas on Louis, in the thought that he would take in each in turn as winter residence: Doué-la-Fontaine in today's Anjou, Ebreuil in Allier, Angeac-Charente, and the disputed Cassinogilum. Charlemagne's intention was to see all his sons brought up as natives of their given territories, wearing the national costume of the region and ruling by the local customs. Thus were the children sent to their respective realms at so young an age. Each kingdom had its importance in keeping some frontier, Louis's was the Spanish March. In 797, Barcelona, the greatest city of the Marca, fell to the Franks when Zeid, its governor, rebelled against Córdoba and, failing, handed it to them. The Umayyad authority recaptured it in 799. However, Louis marched the entire army of his kingdom, including Gascons with their duke Sancho I of Gascony, Provençals under Leibulf, and Goths under Bera, over the Pyrenees and besieged it for two years, wintering there from 800 to 801, when it capitulated.[4] The sons were not given independence from central authority, however, and Charlemagne ingrained in them the concepts of empire and unity by sending them on military expeditions far from their home bases. Louis campaigned in the Italian Mezzogiorno against the Beneventans at least once.

Charlemagne crowns Louis the Pious

Louis was one of Charlemagne's three legitimate sons to survive infancy. He had a twin brother, Lothair who died during infancy. According to Frankish custom, Louis had expected to share his inheritance with his brothers, Charles the Younger, King of Neustria, and Pepin, King of Italy. In the Divisio Regnorum of 806, Charlemagne had slated Charles the Younger as his successor as emperor and chief king, ruling over the Frankish heartland of Neustria and Austrasia, while giving Pepin the Iron Crown of Lombardy, which Charlemagne possessed by conquest. To Louis's kingdom of Aquitaine, he added Septimania, Provence, and part of Burgundy. However, Charlemagne's other legitimate sons died – Pepin in 810 and Charles in 811 – and Louis alone remained to be crowned co-emperor with Charlemagne in 813. On his father's death in 814, he inherited the entire Frankish kingdom and all its possessions (with the sole exception of Italy, which remained within Louis's empire, but under the direct rule of Bernard, Pepin's son).

While at his villa of Doué-la-Fontaine, Anjou, Louis received news of his father's death.[5] He rushed to Aachen and crowned himself emperor to shouts of Vivat Imperator Ludovicus by the attending nobles.[5]

Upon arriving at the imperial court in Aachen, one of Louis' first acts was to purge the palace of its “filth.” He destroyed the old Germanic pagan tokens and texts which had been collected by Charlemagne. He further exiled members of the court he deemed morally “dissolute,” including some of his own relatives.[6]

From the start of his reign, his coinage imitated his father Charlemagne's portrait, which gave it an image of imperial authority and prestige.[5] He quickly sent all of his unmarried sisters to nunneries, to avoid any possible entanglements from overly powerful brothers-in-law.[5] Sparing his illegitimate half-brothers, he forced his father's cousins, Adalard and Wala to be tonsured, placing them in Noirmoutier and Corbie, respectively, despite the latter's initial loyalty.[7]

He also employed Benedict of Aniane (the Second Benedict), a Septimanian Visigoth and monastic founder, to help him reform the Frankish church. One of Benedict's primary reforms was to ensure that all religious houses in Louis' realm adhered to the Rule of Saint Benedict, named for its creator, Benedict of Nursia (480–550), the First Benedict.

On Maundy Thursday 817 (9 April), Louis and his court were crossing a wooden gallery from the cathedral to the palace in Aachen when the gallery collapsed, killing many. Louis, having barely survived and feeling the imminent danger of death, began planning for his succession; three months later he issued an Ordinatio Imperii, an imperial decree that laid out plans for an orderly succession. In 815, he had already given his two eldest sons a share in the government, when he had sent his elder sons Lothair and Pepin to govern Bavaria and Aquitaine respectively, though without the royal titles. Now, he proceeded to divide the empire among his three sons:

Lothair was proclaimed and crowned co-emperor in Aachen by his father. He was promised the succession to most of the Frankish dominions (excluding the exceptions below), and would be the overlord of his brothers and cousin.

Pepin was proclaimed King of Aquitaine, his territory including Gascony, the march around Toulouse, and the counties of Carcassonne, Autun, Avallon and Nevers.

Louis, the youngest son, was proclaimed King of Bavaria and the neighbouring marches.

If one of the subordinate kings died, he was to be succeeded by his sons. If he died childless, Lothair would inherit his kingdom. In the event of Lothair dying without sons, one of Louis the Pious' younger sons would be chosen to replace him by "the people". Above all, the Empire would not be divided: the Emperor would rule supreme over the subordinate kings, whose obedience to him was mandatory.

With this settlement, Louis tried to combine his sense for the Empire's unity, supported by the clergy, while at the same time providing positions for all of his sons. Instead of treating his sons equally in status and land, he elevated his first-born son Lothair above his younger brothers and gave him the largest part of the Empire as his share.

The ordinatio imperii of Aachen left Bernard of Italy in an uncertain and subordinate position as king of Italy, and he began plotting to declare independence upon hearing of it. Louis immediately directed his army towards Italy, and betook himself to Chalon-sur-Saône. Intimidated by the emperor's swift action, Bernard met his uncle at Chalon, under invitation, and surrendered. He was taken to Aachen by Louis, who there had him tried and condemned to death for treason. Louis had the sentence commuted to blinding, which was duly carried out; Bernard did not survive the ordeal, however, dying after two days of agony. Others also suffered: Theodulf of Orléans, in eclipse since the death of Charlemagne, was accused of having supported the rebellion, and was thrown into a monastic prison, dying soon afterwards; it was rumored that he had been poisoned.[8] The fate of his nephew deeply marked Louis's conscience for the rest of his life.

In 822, as a deeply religious man, Louis performed penance for causing Bernard's death, at his palace of Attigny near Vouziers in the Ardennes, before Pope Paschal I, and a council of ecclesiastics and nobles of the realm that had been convened for the reconciliation of Louis with his three younger half-brothers, Hugo whom he soon made abbot of St-Quentin, Drogo whom he soon made Bishop of Metz, and Theodoric. This act of contrition, partly in emulation of Theodosius I, had the effect of greatly reducing his prestige as a Frankish ruler, for he also recited a list of minor offences about which no secular ruler of the time would have taken any notice. He also made the egregious error of releasing Wala and Adalard from their monastic confinements, placing the former in a position of power in the court of Lothair and the latter in a position in his own house.

At the start of Louis's reign, the many tribes – Danes, Obotrites, Slovenes, Bretons, Basques – which inhabited his frontierlands were still in awe of the Frankish emperor's power and dared not stir up any trouble. In 816, however, the Sorbs rebelled and were quickly followed by Slavomir, chief of the Obotrites, who was captured and abandoned by his own people, being replaced by Ceadrag in 818. Soon, Ceadrag too had turned against the Franks and allied with the Danes, who were to become the greatest menace of the Franks in a short time.

A greater Slavic menace was gathering on the southeast. There, Ljudevit, duke of Pannonia, was harassing the border at the Drava and Sava rivers. The margrave of Friuli, Cadolah, was sent out against him, but he died on campaign and, in 820, his margarvate was invaded by Slovenes. In 821, an alliance was made with Borna, duke of the Dalmatia, and Liudewit was brought to heel. In 824 several Slav tribes in the north-western parts of Bulgaria acknowledged Louis's suzerainty and after he was reluctant to settle the matter peacefully with the Bulgarian ruler Omurtag, in 827 the Bulgarians attacked the Franks in Pannonia and regained their lands.

On the far southern edge of his great realm, Louis had to control the Lombard princes of Benevento whom Charlemagne had never subjugated. He extracted promises from Princes Grimoald IV and Sico, but to no effect.

On the southwestern frontier, problems commenced early when c. 812, Louis the Pious crossed the western Pyrenees 'to settle matters' in Pamplona. The expedition made its way back north, where it narrowly escaped an ambush attempt arranged by the Basques in the pass of Roncevaux thanks to the precautions he took, i.e. hostages. Séguin, duke of Gascony, was then deposed by Louis in 816, possibly for failing to suppress or collaborating with the Basque revolt south of the western Pyrenees, so sparking off a Basque uprising that was duly put down by the Frankish emperor in Dax. Seguin was replaced by Lupus III, who was dispossessed in 818 by the emperor. In 820 an assembly at Quierzy-sur-Oise decided to send an expedition against the Cordoban caliphate (827). The counts in charge of the army, Hugh, count of Tours, and Matfrid, count of Orléans, were slow in acting and the expedition came to naught.

In 818, as Louis was returning from a campaign to Brittany, he was greeted by news of the death of his wife, Ermengarde. Ermengarde was the daughter of Ingerman, the duke of Hesbaye. Louis had been close to his wife, who had been involved in policymaking. It was rumoured that she had played a part in her nephew's death and Louis himself believed her own death was divine retribution for that event. It took many months for his courtiers and advisors to convince him to remarry, but eventually he did, in 820, to Judith, daughter of Welf, count of Altdorf. In 823 Judith gave birth to a son, who was named Charles.

The birth of this son damaged the Partition of Aachen, as Louis's attempts to provide for his fourth son met with stiff resistance from his older sons, and the last two decades of his reign were marked by civil war.

At Worms in 829, Louis gave Charles Alemannia with the title of king or duke (historians differ on this), thus enraging his son and co-emperor Lothair,[9] whose promised share was thereby diminished. An insurrection was soon at hand.

With the urging of the vengeful Wala and the cooperation of his brothers, Lothair accused Judith of having committed adultery with Bernard of Septimania, even suggesting Bernard to be the true father of Charles. Ebbo and Hildwin abandoned the emperor at that point, Bernard having risen to greater heights than either of them. Agobard, Archbishop of Lyon, and Jesse, bishop of Amiens, too, opposed the redivision of the empire and lent their episcopal prestige to the rebels.

In 830, at Wala's insistence that Bernard of Septimania was plotting against him, Pepin of Aquitaine led an army of Gascons, with the support of the Neustrian magnates, all the way to Paris. At Verberie, Louis the German joined him. At that time, the emperor returned from another campaign in Brittany to find his empire at war with itself. He marched as far as Compiègne, an ancient royal town, before being surrounded by Pepin's forces and captured. Judith was incarcerated at Poitiers and Bernard fled to Barcelona.

Then Lothair finally set out with a large Lombard army, but Louis had promised his sons Louis the German and Pepin of Aquitaine greater shares of the inheritance, prompting them to shift loyalties in favour of their father. When Lothair tried to call a general council of the realm in Nijmegen, in the heart of Austrasia, the Austrasians and Rhinelanders came with a following of armed retainers, and the disloyal sons were forced to free their father and bow at his feet (831). Lothair was pardoned, but disgraced and banished to Italy.

Pepin returned to Aquitaine and Judith – after being forced to humiliate herself with a solemn oath of innocence – to Louis's court. Only Wala was severely dealt with, making his way to a secluded monastery on the shores of Lake Geneva. Although Hilduin, abbot of Saint Denis, was exiled to Paderborn and Elisachar and Matfrid were deprived of their honours north of the Alps; they did not lose their freedom.[citation needed]

The next revolt occurred a mere two years later (832). The disaffected Pepin was summoned to his father's court, where he was so poorly received he left against his father's orders. Immediately, fearing that Pepin would be stirred up to revolt by his nobles and desiring to reform his morals, Louis the Pious summoned all his forces to meet in Aquitaine in preparation of an uprising, but Louis the German garnered an army of Slav allies and conquered Swabia before the emperor could react. Once again the elder Louis divided his vast realm. At Jonac, he declared Charles king of Aquitaine and deprived Pepin (he was less harsh with the younger Louis), restoring the whole rest of the empire to Lothair, not yet involved in the civil war. Lothair was, however, interested in usurping his father's authority. His ministers had been in contact with Pepin and may have convinced him and Louis the German to rebel, promising him Alemannia, the kingdom of Charles.

Soon Lothair, with the support of Pope Gregory IV, whom he had confirmed in office without his father's support, joined the revolt in 833. While Louis was at Worms gathering a new force, Lothair marched north. Louis marched south. The armies met on the plains of the Rothfeld. There, Gregory met the emperor and may have tried to sow dissension amongst his ranks. Soon much of Louis's army had evaporated before his eyes, and he ordered his few remaining followers to go, because "it would be a pity if any man lost his life or limb on my account." The resigned emperor was taken to Saint-Médard de Soissons, his son Charles to Prüm, and the queen to Tortona. The despicable show of disloyalty and disingenuousness earned the site the name Field of Lies, or Lügenfeld, or Campus Mendacii, ubi plurimorum fidelitas exstincta est.[10]

On 13 November 833, Ebbo of Rheims presided over a synod in the Church of Saint Mary in Soissons which deposed Louis and forced him to publicly confess many crimes, none of which he had, in fact, committed. In return, Lothair gave Ebbo the Abbey of Saint Vaast. Men like Rabanus Maurus, Louis' younger half-brothers Drogo and Hugh, and Emma, Judith's sister and Louis the German's new wife, worked on the younger Louis to make peace with his father, for the sake of unity of the empire. The humiliation to which Louis was then subjected at Notre Dame in Compiègne turned the loyal barons of Austrasia and Saxony against Lothair, and the usurper fled to Burgundy, skirmishing with loyalists near Chalon-sur-Saône. Louis was restored the next year, on 1 March 834.

In 836, however, the family made peace and Louis restored Pepin and Louis, deprived Lothair of all save Italy, and gave it to Charles in a new division, given at the diet of Crémieu. At about that time, the Vikings terrorised and sacked Utrecht and Antwerp. In 837, they went up the Rhine as far as Nijmegen, and their king, Rorik, demanded the wergild of some of his followers killed on previous expeditions before Louis the Pious mustered a massive force and marched against them. They fled, but it would not be the last time they harried the northern coasts. In 838, they even claimed sovereignty over Frisia, but a treaty was confirmed between them and the Franks in 839. Louis the Pious ordered the construction of a North Sea fleet and the sending of missi dominici into Frisia to establish Frankish sovereignty there.

In 837, Louis crowned Charles king over all of Alemannia and Burgundy and gave him a portion of his brother Louis' land. Louis the German promptly rose in revolt, and the emperor redivided his realm again at Quierzy-sur-Oise, giving all of the young king of Bavaria's lands, save Bavaria itself, to Charles. Emperor Louis did not stop there, however. His devotion to Charles knew no bounds. When Pepin died in 838, Louis declared Charles the new king of Aquitaine. The nobles, however, elected Pepin's son Pepin II. When Louis threatened invasion, the third great civil war of his reign broke out. In the spring of 839, Louis the German invaded Swabia, Pepin II and his Gascon subjects fought all the way to the Loire, and the Danes returned to ravage the Frisian coast (sacking Dorestad for a second time).

Lothair, for the first time in a long time, allied with his father and pledged support at Worms in exchange for a redivision of the inheritance. At a final placitum held there, Louis gave Bavaria to Louis the German and disinherited Pepin II, leaving the entire remainder of the empire to be divided roughly into an eastern part and a western. Lothair was given the choice of which partition he would inherit and he chose the eastern, including Italy, leaving the western for Charles. The emperor quickly subjugated Aquitaine and had Charles recognised by the nobles and clergy at Clermont-en-Auvergne in 840. Louis then, in a final flash of glory, rushed into Bavaria and forced the younger Louis into the Ostmark. The empire now settled as he had declared it at Worms, he returned in July to Frankfurt am Main, where he disbanded the army. The final civil war of his reign was over.[citation needed]

Louis fell ill soon after his final victorious campaigns and went to his summer hunting lodge on an island in the Rhine, by his palace at Ingelheim. On 20 June 840, he died, at the old age of 62, in the presence of many bishops and clerics and in the arms of his half-brother Drogo, though Charles and Judith were absent in Poitiers. Soon dispute plunged the surviving brothers into a civil war that was only settled in 843 by the Treaty of Verdun, which split the Frankish realm into three parts, to become the kernels of France and Germany, with Burgundy and the Low Countries between them. The dispute over the kingship of Aquitaine was not fully settled until 860.[citation needed]

^Einhard gives the name of his birthplace as Cassanoilum. In addition to Chasseneuil near Poitiers, scholars have suggested that Louis may have been born at Casseneuil (Lot et Garonne) or at Casseuil on the Garonne near La Réole, where the Dropt flows into the Garonne.

^Paired gold medallions of father and son had been struck on the occasion of the synod of Paris (825) that asserted Frankish claims as emperor, recently denigrated by the Byzantines; see Karl F. Morrison, "The Gold Medallions of Louis the Pious and Lothaire I and the Synod of Paris (825)" Speculum36.4 (October 1961:592–599).